Estimation of the Outer Sphere Contribution to the Activation Parameters for Homogeneous Electron Transfer Reactions Using the Mean Spherical Approximation

1991 ◽  
Author(s):  
W. R. Fawcett ◽  
L. Blum
Keyword(s):  
Electron Transfer ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Transfer Reactions ◽  
Spherical Approximation ◽  
Mean Spherical Approximation ◽  
Electron Transfer Reactions ◽  
The Mean

scholarly journals Reflections on the outer-sphere mechanism of electron transfer

1996 ◽  
Vol 74 (5) ◽  
pp. 631-638 ◽  
Author(s):  
Thomas W. Swaddle
Keyword(s):  
Electron Transfer ◽  
Large Change ◽  
Outer Sphere ◽  
Pressure Effects ◽  
Spherical Approximation ◽  
Mean Spherical Approximation ◽  
Redox Kinetics ◽  
Electron Transfer Processes ◽  
Low Pressures

The quantitative efficacy of the Stranks–Marcus–Hush theory of volumes of activation ΔV‡ for outer-sphere electron transfer between metal complexes in solution is assessed. The theory predicts ΔV‡ accurately for several couples in aqueous solution, but is satisfactory for polar nonaqueous solvents only at pressures of ca. 100 MPa and above, and accuracy is not improved when the molecular nature of the solvent is allowed for through the Mean Spherical Approximation approach. At low pressures, the calculations become numerically unstable when the isothermal compressibility of the solvent is high and its relative permittivity is low, particularly for the more highly charged couples. For aqueous systems, departures from the predicted ΔV‡ afford insights into the role of the counterions, the incursion of inner-sphere pathways, the enhanced reactivity of CoIII/II cage complexes relative to conventional chelates, and the question of "spin forbiddenness" of electron transfer processes that involve a large change in spin multiplicity. Key words: redox kinetics, inorganic reaction mechanisms, pressure effects, Marcus–Hush theory, activation volumes.

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